Safety paper and method of making same



Patented Sept. 12, 1939 UNITED STATES SAFETY PAPER. METHOD OF MAKING Francis L. Simona, Needham, Mass assignor to George La Monte & Son, Nutley, N. 8., a cornotation of New Jersey No Drawing. Application February 4, 1935,

, Serial N0. 4,871

8 Claims. (01. ill-67.95)

This invention relates to safety paper, including fraud-preventing writing material made of paper or other substance or composition adapted for printing or lithographing or for the inscription of writing thereon and for use, for example, in the manufacture of checks, drafts, bonds, stock certificates, or other instruments, which it is desired to haveprotected against fraudulent alteration and to methods of making such safety paper.

10 This invention relates particularly to safety paper having incorporated therein by impregnation or superficial application, either continuously or 10:-

cally, a 'chemical compound which is adapted upon application of a chemical ink eradieator l5 thereto, to result in a disfiguring stain of a relatively permanent and indelible character which renders apparent attempts that are made to alter the safety paper by the use of a chemical ink eradicator.

It is a purpose of, this invention to aflord chemicals which, when incorporated in safety paper, develop disfiguring stains as aforesaid of a very desirably pronounced and permanent. character when chemical ink eradicators are applied there- 5 to. By developing color, it is meant either that a colorless compound becomes colored, or that a colored compound becomes more intensely colored or changes in color. It is a further purpose of this invention to afford safety paper which does not discolor undesirably on ageing due to premature development of color as the result ofv such causes asexposure to air and/or to light.

I have found that desirable safety paper can be prepared using as a safety chemical a thiourea substance of the kind defined 'hereinbelow. Thiourea substances of the kind below defined, when incorporated in safety paper, have been found to be acted upon by chemical ink eradicators such as the bleaching type of ink eradi- 0 cators so extensively used at the present time, for example, ink eradicators containing sodium hypochlorite, to produce. relatively permanent and indelible colored compounds that immediately disfigure the safety paper and give evidence of the fact that the safety paper has been tampered with. Thus when examples of thiourea substances such as monophenyl thiourea, s-diphenyl thiourea, or diorthotolyl thiourea, and the like, are incorporated in safety paper, the

application of a chemical eradicator containing a substance suchas a hypochlorite or bleaching powder capable of liberating chlorine results in the formation 'of telltale brown stains. The thiourea substances which may be employedin the practice of this invention are substituted thioureas in which one or more of the hydrogens of an amino group is replaced by a radical which tive of an aromatic or heterocyclic hydrocarbon radical, or a salt of a basic derivative of an aromatic or heterocyclic hydrocarbon radical. 10

By an acidic derivative of a hydrocarbon radical, it is understood that one of the hydrogen atoms in'the hydrocarbon radical has been replaced by an acid radical, the acidic radical substituent being limited to the acid radicals SOaH l5 (sulphonic), NOflnitro), COOH (carboxyl) and C1,; Br, or I (halogen). The acidic derivatives of aromatic or heterocyclic hydrocarbon radicals with the possible exception of the halogens form salts with alkali metals and with other salt form- 59 ing. alkaline earths and heavy metals. Thus, for example, the sodium salt of the sulphonic radical is SOaNA as in diorthotolyl thiourea sulphonic acid. The term salts is to be given a broad interpretation as covering organic salts or esters 25 as well as metallic salts. Thus, for example, the sulphonic radical maybe converted into the methyl sulphon'ate SOaCHa. Other organic salts such as ethyl, phenyl, pyridyl, etc., may be formed with the acidic derivatives of aromatic so and heterocyclic hydrocarbon substituents of thiourea.

By a basic derivative ofan aromatic and heterocyclic hydrocarbon radical, it is understood that one of the hydrogen atoms of the hydrocar- 35 bon radical is replaced by a basic radical such as an NH: (amino) radical. Such basic derivatives form salts thereof such as the sulphate, acetate, oxalate and the like.

The aromatic and heterocyclic hydrocarbon 40 substitution products of thiourea which are preferably employed contain as hydrocarbon radicals such aromatic radicals as phenyl, naphthyl, tolyl, etc., and/or such heterocyclic radicals as pyridyl, pyryl, quinolyl, etc. The substituted thioureas 45 containing such hydrocarbon radicals are for the most part insoluble in water. Increased solubility in water is afforded by utilizing the acidic derivatives of aromatic and heterocyclic hydrocarbon radicals and preferably the sulphonic derivative. Increased solubility in water is likewise afforded by utilizing the alkali metal salts of the acidic derivatives of the aromatic or heterocyclic hydrocarbon radicals as substituents in thiourea. For 5| example, the sodium or potassium sulphonates are especially desirable.

Thiourea substances such as monophenyl thiourea, s-diphenyl thiourea, and diorthotolyl thiourea are substantially colorless; that is, they donot impart substantial color to safety paper in which they are incorporated when used in amounts suflicient to impart substantial protection to the safety paper. The use of substantially colorless compounds is regarded as preferable in the practice of this invention. Such safety chemicals are also comparatively inexpensive.

For purposes of explanation and of defining .certain thiourea substances adapted to be incorporated in safety paper in the practice of this invention, reference is made to the following general formula: v

\NCSN/ wherein one of the radicals R, R1, R2, and R3 may be any radical selected from the group consisting of aromatic and heterocyclic hydrocarbon radicals, acidic derivatives of such hydrocarbon radicals, salts of said acidic, derivatives, basic derivatives of such hydrocarbon radicals, salts of said basic derivatives, and hydrogen, at least one of the radicals R, R1, R2, and R3 being other than hydrogen.

If more than one of the raicals R, R1, R2 and R3 are other than hydrogen, the formula may assume various. forms. Thus a substance such as diphenyl thiourea may either be symmetrical or unsymmetrical. For example, the formula of diphenyl thiourea may be either NH2CSN(CeI-I5)z (unsymmetrical) CsH5NHCSNHCsH5 (symmetrical) In the foregoing formulas, the acidic derivatives are normally preferred to the basic derivatives of the aromatic and heterocyclic hydrocarbon radicals, and of the acidic derivatives the sulphonic and carboxylic derivatives are preferred. It is understood that the hydroxy derivatives are not included in the acidic or basic derivatives of the aromatic and heterocyclic hydrocarbon radicals. Of the salts of the acid derivatives, the alkali metal salts are preferred.

The stain produced by applying an oxidizing agent to safety paper containing the chemicals above mentioned are relatively permanent in their ability to withstand treatment with acids or alkalis or reducing agents.

Further features of this invention reside in incorporating in, safety paper a chemical substance which is in itself of suflicient stability to resist discoloration upon ageing but which is con verted into a substance, which may be less stable, by the action "of a chemical ink eradicator thereon. The latter substance is then in turn acted upon by the chemical ink eradicator to produce a colored compound. Sensitive chemical substances have been known heretofore which are adapted to react under the influence of chemical eradicators to produce colored compounds, but very many of such chemicals have been unsuitable lor commercial use in safety paper due to the fact that on ageing they become changed to colored compounds, with the result that safety paper becomes undesirably discolored and in certain cases entirely ruined.

The hiourea substances above mentioned afford examples of the features just discussed.

Thus, when a thiourea substance of the type referred to above is treated with a bleaching material, it is converted into another substance which is believed to be an amino thiazole. Amino thiazoles are not in themselves necessarily colored so as to stain safety paper. However, the amino thiazoles are sensitive chemicals which are thrown down by hpochlorites, free chlorine, and the like, into colored bodies that give the desired telltale indicia of attempted alteration. In the above manner, one of the greatest dimculties in so-called sensitive chemicals has been removed, as very many of such chemicals tend to turn dark on standing or on exposure to light. Instead of using a sensitive chemical directly, I use a chemical which is stable against ageing but which under the influence of a. chemical ink eradicator is converted into a second substance that, in turn is changed by the ink eradicator to produce a telltale stain. Thus, even though the second chemical is unstable against ageing, the safety paper is rendered resistant to deterioration due to the fact that chemical originally incorporated in the safety paper does not tend to change to the second or intermediate chemical except as the result of applying a chemical ink eradicator thereto.

While the thiourea substances above mentioned under the influences of chemical bleaching compounds have the property of being converted into intermediate compounds which in turn are converted into relatively indelible colored compounds, I have'found that the reaction can be made to proceed more vigorously with .the development of more pronounced colorwhen there is present in the paper an alkali metal bromide such as sodium or potassium bromide.

While the alkali bromide does not cause premature development of color prior to the application of the bleaching compound, nevertheless when the bleaching compound is applied to safety paper containing a thiourea substance of the type above referred to, together with an alkali metal bromide, the presence of the alkali metal bromide results in a more vigorous color development than where it is not employed. This result is believed to be due to a specific action of bro- -type of ink eradicator to the safety paper. and

more highly colored stains are produced.

The preparation of safety paper embodying this invention may be accomplished in several ways. water-insoluble compounds such as monophenyl thiourea, s-diphenyl thiourea and diorthotolyl thiourea may be incorporated in safety paper by mixing the same with the paper ,flber during the beating process that is part of the manufacture-of paper. They may be added in the form of dry powder, for example-as they are very stable. In such case, during the paperried into the paper. In the case of phenyl thiourea and diorthotolyl thiourea, about two per making operation, the safety chemical is carcent. to ten per cent. on the dry weight of the' use of water-soluble thiourea substances is repaper may be used. Of course, greater or lesser .amounts can be used, depending on the colorareaction desired in the finished safety paper.-

Usually, the more of the chemical incorporated in the safety paper, the more intense will the color reaction be when a chemical bleach is applied to the safety paper.

Alternatively, the safety chemical may be dissolved in a suitable solvent therefor. Thus many of the thioureas are soluble in solvents such as acetone, ethyl alcohol, benzene and the like or mixtures thereof. A solution of the safety chemical may be applied in any suitable manner as by dipping, spraying, etc. If a water-soluble thiourea substance of the kind above referred to is employed. the solvent used may be water. The

that is likewise incorporated in the safety paper.

This may be done in any suitable way as by running the pa r through a bath containing the alkali metal bromide dissolved in water, for example. When a water-soluble thiourea substance is used, the thiourea substance and alkali metal bromide may be conveniently applied as dissolved in the same bath.

The safety chemicals above'described, by the methods above described or by other methods of impregnation or surface application; can be impregnated in the body of the safety paper or may be applied at a. surface thereof, and, while it is -preferable to have all parts of the safety paper reactive similarly in the development of colored warning indicia under the influence of a chemical ink eradicator, the safety chemicals can be applied locally as by printing or otherwise. In any event, safety'paper carrying the safety chemicals herein described will be regarded as having suchsafety chemicals incorporated therein.

} It will be understood that this invention is applicable among other fields of application in connection with plain white paper as well as tinted paper or paper having surface markings thereon. It is likewise applicable when a tint in the paper is delible under the action of chemical ink eradicatcrs and/or when the surface marking or tinting is removable by mechanical erasure.

While this invention has been described in connection with certain specific examples thereof,

it is to'be understood that this has been done merely for the purpose of illustration and that the scope of this invention is to be governed by the following claims.

I claim:

1. A safety paper having incorporated therewith a substituted thiourea containing an aromatic or heterocyclic substituent and an alkali metal bromide.

2. A safety paper having incorporated therein diphenyl thiourea. 1

3. A safety paper having incorporated therein an alkali metal bromide and diphenyl thiourea.

4. A safety paper having incorporated therein an alkali metal bromide and diorthotolyl thiourea sulphonic acid.

5. A safety paper having incorporated therein an alkali metal bromide and amino naphthyl thiourea.

6. A method of making safety paper which comprises incorporating therein diphenyl thiourea.

7. A safety paper having incorporated therein an alkali metal bromide and a substance having the formula R\ R! No 8 N/ wherein each of the radicals R, R1, R2, and R3 is selected fromthe group consisting of aromatic and heterocyclic hydrocarbon radicals, acidic derivatives of such hydrocarbon radicals containing acid radicals selected from the group consisting of SOaH, N02, COOH, Cl, Br and I including salts thereof, basic derivatives of such hydrocarbon radicals, salts of said basic derivatives and hydrogen, at least one of the radicals R, R1, R2 and Ra being other than hydrogen.

8. A method of making safety paper which comprises incorporating therein an alkali metal bromide and a substance having the formula 

